1. Field of the Invention
The present invention relates to a substrate for use to make a thin-film magnetic head slider for a hard disk drive (which will be referred to herein as a “thin-film magnetic head substrate”) and also relates to a method of manufacturing such a substrate.
2. Description of the Related Art
Thanks to recent tremendous development of information and telecommunication technologies, the amount of information that can be processed by computers has increased by leaps and bounds. In particular, audiovisual (or multimedia) information such as audio, music and video, which used to be capable of being processed only as analog signals, now can be converted into digital signals and processed by personal computers. Multimedia data such as music and video contains a huge amount of information. Thus, it has become more and more necessary to further increase the capacity of information storage devices for use in personal computers, for example.
A hard disk drive is a typical information storage device that has been used broadly in personal computers, for example. To meet the demand described above, the capacity of hard disks needs to be further increased and the overall size of the drive needs to be reduced. Meanwhile, a hard disk recorder for writing video data on a hard disk directly and an audio player for writing musical data on a hard disk have become increasingly popular these days. In these recorders and players, the storage capacity also needs to be further increased and the overall size of the hard disk drive also needs to be decreased to make the recorder or player ready to carry about.
FIGS. 7(a) & 7(b) are a cross-sectional view schematically illustrating a thin-film magnetic head slider and surrounding portions thereof in a conventional hard disk drive. As shown in FIGS. 7(a) & 7(b), an undercoat film 13 is provided on a side surface of a base 12, which is supported on a gimbal 10. A read device 16 is provided as a read head on the undercoat film 13 and a write device 14 is further provided as a write head adjacent to the read device 16. Such a unit, including the base 12, write device 14 and read device 16 to be supported on the gimbal 10, is normally called a “head slider” or simply “slider”.
The write device 14 is made of a magnetic material and has a ring configuration, inside of which a coil 15 is wound. When a write signal is supplied to the coil 15, a magnetic field is generated in the write device 14, thereby writing data on a magnetic storage medium 17.
On the other hand, the read device 16 as a read head is a magneto-resistive (MR) or giant MR (GMR) element to convert a variation in magnetic field into a variation in electrical resistance. That is to say, the read device 16 senses a variation in the magnetic field recorded on the magnetic storage medium 17 and converts the variation into an electrical signal.
The base 12 to hold the read device 16 and the write device 14 thereon has often been made of an Al2O3—TiC based ceramic sintered body. The Al2O3—TiC based ceramic material (which will be referred to herein as an “AlTiC material”) has been used extensively because this material exhibits excellent thermal and mechanical properties and processibility while striking an adequate balance between them. However, the AlTiC material is a good electrical conductor. Accordingly, if a read/write device 14′ or the write device 14 were disposed adjacent to such a conductor base 12, then the read device 16 or write device 14 would be short-circuited and could not operate properly. Also, the surface of such an AlTiC base is not sufficiently smooth. For that reason, to electrically insulate the read device 16 or write device 14 from the base 12 sufficiently and increase the smoothness of the surface of the base 12, the undercoat film 13 of Al2O3 is normally provided on the side surface of the base 12. This is because Al2O3 exhibits a good electrical insulation property and has a smooth enough surface.
The conventional slider, however, has various problems to overcome.
Firstly, as it has become more and more necessary to reduce the overall size of hard disk drives, sliders also must be further reduced in size. To reduce the size of sliders, the cross-sectional area of the coil 15 inside of the write device 14 should be reduced as shown in FIG. 7(b). More specifically, the inside diameter of the coil 15 needs to be minimized and yet respective loops of the coil 15 should not overlap with each other. However, when a current flows through the coil 15 with such a reduced cross-sectional area by way of terminals 18, the quantity of heat generated per unit area increases.
However, Al2O3, which has often been used as a material for the undercoat film 13, does not have so good thermal conductivity as AlTiC. Accordingly, the heat, generated by supplying the coil 15 with current, is shut off by the Al2O3 undercoat film 13, and cannot diffuse toward the base 12 sufficiently. Thus, the heat is stored in the read device 16 or the write device 14. As a result, the read device 16 or the write device 14 thermally expands to possibly cause read errors or write errors.
To overcome this problem, the undercoat film 13 may have a reduced thickness so that the heat can be dissipated into the base 12 more easily. In that case, however, the dielectric breakdown strength might decrease, which is another problem to overcome.
To stabilize the characteristics of an MR device fabricated on an undercoat film of Al2O3, the undercoat film is required to have a smooth surface. For that purpose, in the prior art, the Al2O3 film, deposited on a ceramic base, is subjected to a CMP or any other process to planarize the surface of the undercoat film of Al2O3. Also, to increase the degree of adhesiveness, normally an inverse sputtering process may be carried out before the Al2O3 film is deposited on an AlTiC base or a sputtering process may be carried out with a bias voltage applied (which is called a “bias sputtering process”) while the Al2O3 film is being deposited. If the inverse sputtering process or the bias sputtering process is carried out, then the surface to deposit a film thereon is etched.
The AlTiC base is a composite sintered body of dissimilar materials (i.e., Al2O3 and TiC), which have mutually different etch rates. For that reason, the crystal level differences on the surface of the AlTiC base further expand as a result of the inverse or bias sputtering process. The Al2O3 undercoat film just deposited may have a surface roughness Ra of about 1 nm to about 5 nm. However, the thinner the undercoat film gets (e.g., comes to have a thickness of 0.4 μm or less), the more difficult it is to perform the planarization process.
To overcome these problems, Japanese Patent Application Laid-Open Publication No. 11-283221 discloses that a conventional undercoat film 13 is provided on a base 12 and an amorphous alumina film is deposited to a thickness of 100 nm to 55,000 nm on the undercoat film 13 by an ECR sputtering process. Japanese Patent Application Laid-Open Publication No. 11-283221 insists that high dielectric breakdown strength is achieved by such a structure because the amorphous alumina film deposited by the ECR sputtering process has high density.
However, to obtain such a structure, an ECR sputtering system needs to be used. That is to say, two different types of systems need to be used to make the conventional undercoat film 13 and that amorphous alumina film, respectively, thus increasing the manufacturing cost of the substrate significantly.    Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 11-283221    Patent Document No. 2: Japanese Patent No. 1899891    Patent Document No. 3: U.S. Pat. No. 4,796,127    Patent Document No. 4: Japanese Patent No. 1659501    Patent Document No. 5: U.S. Pat. No. 4,814,915    Patent Document No. 6: Japanese Patent Application Laid-Open Publication No. 2000-260009